Tonantzitlolone is a Nanomolar Potency Activator of TRPC1/4/5 Channels.

BACKGROUND AND PURPOSE

The diterpene ester tonantzitlonone (TZL) is a natural product which displays cytotoxicity towards certain types of cancer cell such as renal cell carcinoma cells. The effect is similar to that of (‐)‐Englerin A (EA) and so, although it is chemically distinct, we investigated whether TZL also targets transient receptor potential canonical (TRPC) channels of the TRPC1, TRPC4 and TRPC5 type (TRPC1/4/5 channels).

EXPERIMENTAL APPROACH

Renal cell carcinoma A498 cells natively expressing TRPC1 and TRPC4, modified HEK 293 cells over expressing TRPC4, TRPC5, TRPC4‐TRPC1 or TRPC5‐TRPC1 concatemer, TRPC3 or TRPM2 or CHO cells over expressing TRPV4 were studied by intracellular Ca2+ measurement or whole‐cell or excised membrane patch‐clamp electrophysiology.

KEY RESULTS

TZL evoked intracellular Ca2+ elevation in A498 cells, similar to that evoked by EA. TZL activated overexpressed channels with concentration for 50% activation (EC50) at 123 nM (TRPC4), 83 nM (TRPC5), 140 nM (TRPC4‐TRPC1) and 61 nM (TRPC5‐TRPC1). Effects of TZL were reversible on wash‐out and potently inhibited by the TRPC1/4/5 inhibitor Pico145. TZL activated TRPC5 channels when bath‐applied to excised outside‐out but not inside‐out patches. TZL failed to activate endogenous store‐operated Ca2+ entry in HEK 293 cells or overexpressed TRPC3, TRPV4 or TRPM2 channels.

CONCLUSIONS AND IMPLICATIONS

TZL is a novel potent agonist for TRPC1/4/5 channels which should be useful for testing the functionality of this type of ion channel and understanding how TRPC1/4/5 agonists achieve selective cytotoxicity against certain types of cancer cell.